The term "stent" is generally used to describe endoprothstetic medical devices which are implanted in anatomical passageways (e.g., blood vessels, gastrointestinal tract, genitourinary tract, endocrine ducts, etc . . . ) of the body for the purpose of maintaining the patency or state of dilation of the passageway, reinforcing the passageway, or anchoring a tubular graft or other object within the passageway.
Typically, such stents are implanted in blood vessels to maintain dilation and patency of an occluded region of blood vessel, or to bridge a weakened or aneurysmic region of blood vessel. On the other hand, some typical nonvascular applications of such stents are for the treatment of constrictions or injuries to the gastrointestinal tract (e.g., esophagus), ducts of the biliary tree (e.g., common bile duct) or anatomical passageways of the genitourinary tract (e.g., ureter, urethra fallopian tube, etc.).
Transluminally implantable stents are initially disposed in a compact configuration of relatively small diameter, and are initially mounted upon or within a delivery catheter to facilitate insertion and transluminal advancement of the stent into the desired anatomical passageway. Thereafter, such stents are radially expanded to a larger "operative" diameter which is equal to or slightly larger than the diameter of the anatomical passageway in which the stent is to be implanted. When radially expanded to such operative diameter, the stent will typically become released or separated from the delivery catheter and anchored or frictionally engaged to the surrounding wall of the anatomical passageway.
Some stents have a pliable, continuous tubular covering, in which case they are typically referred to as a "stented graft" or "stent-graft".
In general, stents and stented grafts fall into two major categories--a) self-expanding and b) pressure-expandable. Those of the self-expanding variety may be formed of resilient or shape memory material (e.g., spring steel or nitinol.TM.) which is capable of self-expanding from its first (radially compact) diameter to its second (operative) diameter without the exertion of outwardly-directed force against the stent or stented graft. Examples of such self-expanding stents and stented grafts are set forth in U.S. Pat. No. 4,655,771 (Wallsten, et al); U.S. Pat. No. 4,954,126 (Wallsten); U.S. Pat. No. 5,061,275 (Wallsten, et al); U.S. Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,830,003 (Wolf, et al); U.S. Pat. No. 5,035,706 (Gianturco, et al); U.S. Pat. No. 5,330,400 (Song) and U.S. Pat. No. 5,354,308 (Simon, et al) and Foreign Patent Publication Nos. WO94.backslash.12136; WO92.backslash.06734 and EPA183372. Those of the pressure-expandable (i.e., "passive expandable") variety may be formed of plastically deformable material (e.g., stainless steel) which is initially formed in its first (radially compact) diameter and remains stable in such first diameter until such time outwardly directed pressure is exerted upon the stent or stented graft to cause radial expansion and resultant plastic deformation of the stent or stented graft, to its second (operative) diameter. Examples of such pressure-expandable stents and stented grafts are set forth in U.S. Pat. No. 5,135,536 (Hillstead); U.S. Pat. No. 5,161,547 (Tower); U.S. Pat. No. 5,292,331 (Boneau); U.S. Pat. No. 5,304,200 (Spaulding); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 5,282,823 (Schwartz, et al); U.S. Pat. No. 4,776,337 (Palmaz); and U.S. Pat. No. 5,403,341 (Solar) and Foreign Patent Publication Nos. EPA480667; and WO95.backslash.08966.
In many applications, careful positioning and sound anchoring of the stent or stented graft is critical to the successful treatment of the underlying medical problem. In this regard, the delivery catheter which is utilized to insert and position the stent or stented graft may be an important aspect of the overall system. Various types of delivery catheters for stents and stented grafts have been previously known, including those described in U.S. Pat. No. 4,665,918 (Garza, et al); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,739,762 (Palmaz); U.S. Pat. No. 4,762,125 (Leiman, et al);, U.S. Pat. No. 776,337 (Palmaz); U.S. Pat. No. 4,838,269 (Robinson, et al); U.S. Pat. No. 4,994,071 (MacGregor); U.S. Pat. No. 5,037,427 (Harada, et al); U.S. Pat. No. 5,089,005 (Harada); U.S. Pat. No. 5,102,417 (Palmaz); U.S. Pat. No. 5,108,416 (Ryan, et al); U.S. Pat. No. 5,141,498 (Christian); U.S. Pat. No. 5,181,920 (Mueller, et al); U.S. Pat. No. 5,195,984 (Schatz); U.S. Pat. No. 5,201,901 (Harada, et al); U.S. Pat. No. 5,269,763 (Boehmer, et al); U.S. Pat. No. 5,275,622 (Lazarus, et al); U.S. Pat. No. 5,290,295 (Querals, et al); U.S. Pat. No. 5,306,294 (Winston, et al); U.S. Pat. No. 5,318,588 (Horzewski, et al); U.S. Pat. No. 5,344,426 (Lau, et al); U.S. Pat. No. 5,350,363 (Goode, et al); U.S. Pat. No. 5,360,401 (Turnland); U.S. Pat. No. 5,391,172 (Williams, et al); U.S. Pat. No. 5,397,345 (Lazarus); U.S. Pat. No. 5,405,380 (Gianotti, et al); U.S. Pat. No. 5,443,452 (Hart, et al); U.S. Pat. No. 5,453,090 (Martinez, et al); U.S. Pat. No. 5,456,284 (Ryan, et al); and U.S. Pat. No. 5,456,694 (Marin, et al) and Foreign Patent Publication Nos. EP-0308-815-A2; EP-0335341-A1; EP-364-787-A; EP-0442-657-A2; EP-482976-A; EP-0505686-A1; EP-0611-556-A1; EP-0638-290-A1; WO94.backslash.15549;
WO95.backslash.01761; GB2196-857-A; DE3042-229; and DE3737-121-A.
As previously indicated, many types of stents or stented grafts are currently used in relation to the treatment of various disorders. Perhaps the most common use of stents and stented grafts is in relation to the treatment of narrowed or constricted blood vessels. For these applications, pressure expandable stents are typically employed, with the delivery of the stent to the desired treatment site being facilitated through the use of a delivery catheter including an inflatable balloon which is used to facilitate the radial expansion of the stent positioned thereupon to its final, operative diameter.
In this particular application, two serious problems are known to often occur during the advancement of the stent through the anatomical passageway (e.g., the blood vessel). These problems include the tendency of the stent to slip off of the balloon of the delivery catheter, and occurrences of the stent scraping or otherwise damaging the lining of the anatomical passageway through which the delivery catheter is advanced. Slippage of the stent upon the balloon of the delivery catheter may result in improper placement of the stent within the treatment site, thus requiring the use of additional stents to correct such improper placement. More seriously, such slippage may cause the stent to be "lost", thus giving rise to the risk of the stent embolizing in its unexpanded state. The scraping of the lining of the anatomical passageway (e.g., the intima of an artery) may lead to complications such as spasm, thrombosis and/or perforation of the passageway.
In an attempt to solve these particular problems, delivery catheters constructed in accordance with the prior art often employ sheaths of various designs which are used to cover the stent positioned upon the furled balloon during the advancement of the delivery catheter through the anatomical passageway. In other prior art designs, the stent is mounted over a balloon which is attached to an inner tube, with the inner tube itself residing within an outer tube which acts as a sleeve or sheath. However, these prior art designs which incorporate sheaths or outer tubes which act as sheaths add significant bulk to the delivery catheter, and increase the size and stiffness of the delivery system. Such increased rigidity causes difficulties in navigating the delivery catheter through tortuous anatomical passageways, and thus may interfere with the safe placement of the stent into the desired treatment site. Additionally, in those prior art systems employing an outer tube which acts as a sheath, the outer tube itself creates a surface upon which the end of the stent can inadvertently catch, with the inclusion of the outer tube also making it difficult to determine when the same has been completely retracted or withdrawn from the stent. In this respect, the inclusion of the outer tube creates a manipulative problem regarding whether the stent has been sufficiently exposed prior to its radial expansion. Additionally, the readvancement of the outer tube over the stent is difficult if the stent must be repositioned within the anatomical passageway. Moreover, the inclusion of sheaths or outer tubes in the prior art delivery systems adds costs thereto, and further increases the complexity of the stent placement procedure. The present invention overcomes these prior art deficiencies by providing a delivery system for a stent or stented graft which prevents the stent from slipping and protects the anatomical passageway during stent placement without having the bulk of a sheath or other stent coverings such as an outer tube.